Traps for insects have recently come into use especially since particular attractive substances, such as sexual ferhormones, aggregating ferhormones, phagoattractants, etc., which offer the advantage of specifically attracting only a species without damaging useful species, or animals, or cultivations, have begun to be utilized in order to determine the development or to control the growth of the population of certain infesting or noxious species.
Traps for insects based on such principles are already known. Some of them, for example, are shaped as a box having in the surface delimiting it a number of such entrances or passages, such the insects, in order to reach the inside, must follow a sort of labyrinth or must slip through narrowings, which they are then unable to follow again to get out.
This article has proven to be very useful to catch insects alive, but the box-shaped trap has the drawback of being rather cumbersome and of not assuring the capture of a large number of insects. Many of them, in fact, do not succeed in reaching the inside, or they succeed in escaping through holes that have accidentally formed in the box.
According to a later technique, traps are constructed in which the active principle is placed near or above a liming paste, by which the insect is captured.
This is the principle on which the trap described in French Pat. No. 2,108,486 of Minnesota Mining and Manufacturing Co. is based. This patent illustrates a trap consisting of at least three surfaces radially arranged around a common axis and spread with a sticky substance suitable for capture the insects, the attracting substance being contained inside said surfaces, in suitable containers. The attracting substance may be contained also in a container arranged in the proximity of the axis common to the surfaces spread with the sticky substance.
The surfaces are fixed to the common axis, so that they can be folded against one another, like a book or a cover, so as to have minimum over-all dimensions when the trap is not being used.
This article, although it offers considerable advantages with respect to handling, has nevertheless a serious drawback: it is little fit for exposure to the open air. In fact, the atmospheric agents, such as rain, wind, sun, can wash away, remove and soil the glue-spread surfaces, or can alter the attracting substance which is employed.
Another type of trap is described in German Pat. No. 2,053,869 of said Minnesota Mining and Manufacturing Co. This relates to a trap for insects constructed with a waterproof paperboard plate, that is folded up on itself and can be opened so as to form a parallelepiped-like chamber having two opposite rhomboidal openings.
Such trap is hung by means of an iron wire hook fastened to one of the parallelepiped edges. The shape is retained by folding inwards a part of the trap walls in proximity of the openings. The trap's inside walls are thoroughly coated with glue. The attracting product can be applied onto the glue, in the form of proper formulations, such as, for example, beads of molten paraffin, with which the attractive substance has been admixed.
In this case the trap surface is in an internal position and, by consequence, is protected. Nevertheless, the trap, once placed in the open air, is rapidly damaged by the atmospheric agents due to the material it is made of.